cmd/vendor: upgrade pprof to latest

This change upgrades the vendored pprof to pick up the fix for a
serious issue that made the source view in browser mode blank
(tracked upstream as google/pprof#621).

I also had to patch pprof.go, since one of the upstream commit we
included introduced a breaking change in the file interface (the Base
method is now called ObjAddr and has a different signature).

I've manually verified that the upgrade fixes the aforementioned
issues with the source view.

Fixes #45786

Change-Id: I00659ae539a2ad603758e1f06572374d483b9ddc
Reviewed-on: https://go-review.googlesource.com/c/go/+/318049


Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>